As shown in FIGS. 14A and 14B, a conventional valve apparatus 100 has a valve body 101 which is provided with a seal ring 102 on its outer periphery. This valve apparatus 100 is employed as an EGR-valve apparatus, for example, which varies a quantity of exhaust gas recirculating from an exhaust passage to an intake passage of an internal combustion engine.
The valve apparatus 100 is comprised of a valve nozzle 104 defining a fluid passage 103 therein, a plate-shaped valve body 101 rotatably accommodated in the valve nozzle 104 to vary a fluid passage area of the fluid passage 103, and the seal ring 102 provided on an outer periphery of the valve body 101.
The seal ring 102 seals a clearance gap between the outer periphery of the valve body 101 and an inner wall surface 105 of the fluid passage 103. As shown in FIGS. 15A and 15B, the seal ring 102 is C-shaped and is engaged with an annular groove 106 formed on the outer periphery of the valve body 101 (refer to JP-2007-285311A, for example). The C-shaped seal ring 102 forms an arc clearance 107 between its both ends and forms an annular clearance 108 in cooperation with a bottom surface of the annular groove 106. While forming the above clearances 107, 108, the seal ring 102 is rotated along with the valve body 101.
When the valve body 101 fully closes the fluid passage 103, the seal ring 102 is brought into contact with the inner wall surface 105 and is elastically deformed so that the above clearances 107, 108 are shrunk. At this moment, the seal ring 102 is in contact with the inner wall surface 105 by its tension and is brought into contact with a side wall surface 109 of the annular groove 106 by an exhaust gas pressure.
When the valve body 101 is rotated from a full-close position to a full-open position, a condition of the seal ring 102 varies as shown in FIGS. 16A to 16D.
Specifically, when the valve body 101 starts to rotate around its axis from the full-close position (FIG. 16A), the clearances 107, 108 start to expand. For a specified time period, the seal ring 102 is kept in contact with the inner wall surface 105. Then, when the valve body 101 is rotated to a first boundary angle position (1-BAP), an outer surface of the seal ring 102 is partially apart from the inner wall surface 105, as shown in FIG. 16B.
When the valve body 101 is further rotated from the first boundary angle position toward the full-open position, the tension of the seal ring 102 is decreased and the clearances 107, 108 expand. Then, the valve body 101 is rotated to a second boundary angle position (2-BAP) in which the seal ring 102 has no tension and freely moves in the groove 106, as shown in FIG. 16C.
After that, the valve body 101 is rotated to the full-open position while a free condition of the seal ring 102 is maintained, as shown in FIG. 16D.
When the valve body 101 is rotated from a position where the seal ring 102 is in the free condition toward the full-close position, the seal ring 102 is brought into contact with the inner wall surface 105 with the clearances 107, 108 expanded. Then, the seal ring 102 is elastically deformed in such a manner that the clearances 107, 108 are shrunk.
This forcible contact between the seal ring 102 and the inner wall surface 105 increases abrasions at the contacting portions therebetween. Furthermore, after the seal ring 102 is brought into contact with the inner wall surface 105, the seal ring 102 keeps sliding on the inner wall surface 105 with tension increasing, whereby the abrasions are further increased.